Chemometrics, Health Risk Assessment and Probable Sources of Total Petroleum Hydrocarbons in Atmospheric Rainwater in Rivers State, Nigeria.

16 17 Total petroleum hydrocarbons (TPHs)-(aliphatic and aromatic) were analysed for in atmospheric 18 rainwater between April- June; July – August; September–October depicting early, mid, late rain of 19 2019. Sampling at Rumuodomaya/ Rumuodome and Ogale in Rivers State using basins fastened to a 20 table 2 M above ground and 120 M from high features, Rainwater was analysed after treatment using 21 Agilent GC-FID. Results show cumulative TPHs at R/R were 56.6551mg/L, 39.5201mg/L and 22 7.2283mg/L, Ogale: 9.1217mg/L, 59.4923mg/L and 21.9825mg/L. Aliphatic hydrocarbons: C5 – C8 23 were < 1, low contamination, other carbon aggregates (C9 – C16, C17– C35, and C36 – C40) indicate 24 high contamination. Chemometric assessment showed high contamination. TPHs aggregates at 25 Rumuodomaya/ Rumuodome were- C8 – C11 (1.034 and 1.005) early rain, C18 – C25 and C26 – 26 C33 has Carbon preference index of 1.287 and 1.630 (mid-rain), C26 – C33 has CPI of 1.288 (late- 27 rain), Ogale area, C26–C33 has CPI of 1.732 (early-rain), mid-rain C8 – C11 (2.768) and C12–C17 28 (5.368). Pristane/phytane ratio indicated biogenic and pyrogenic sources. Average carbon length of 29 TPHs for odd n-alkanes were C9 – C11 (9.446) and C35 – C39 (38.980), C9 – C11(10.238), C35 – 30 C39 (36.510); C9 – C11 (10.240) and C35 – C39 (36.934). Average daily intake depicted possible 31 health issues for children and adults as hazard index > 1 for aromatics.


Introduction
1 Rivers State Nigeria has been a petroleum exploration and exploitation hotspot for over 50 years 2 covering a land mass of about 10,575 square kilometres [1]. There is continuous wet and dry season 3 through the year resulting from the impact of the Atlantic Ocean and Sahara Desert continental air 4 masses. Annual rainfall ranges from 1900 -2850 mm, temperature varies from 22.6 -34.0 ºC, relative 5 humidity between 65 -80% [1]. Different local and international oil companies situated onshore and 6 offshore with downstream petroleum depots and filling stations surround major oil-producing 7 communities and connect several pipelines and flow stations. These activities may likely result in the 8 release of environmental contaminants such as polynuclear aromatic hydrocarbons (PHAs), aliphatic 9 hydrocarbons, heavy metals, organometallic compounds, aerosols, ashes, particulates, H2S, COX, 10 NOX, SOX, soot, smoke, etc into the atmosphere as activities of petroleum companies are intense in 11 Nigeria's crude oil and gas-bearing region reputed to house several billions of crude oil and trillions 12 of cubic feet of natural gas [2]. Out of several environmental contaminants that may be released, total 13 petroleum hydrocarbons (TPHs) stand out and are chemical compounds produced by phytogenic 14 (plants, animal and microbes), petrogenic (crude oil, gas, and coal), and pyrogenic (natural and 15 anthropogenic) combustion of carbonaceous component [3]. 16 They are made from carbon and hydrogen compounds that range from C5 -C40 with aromatic (cyclic 17 ring) such as polycyclic aromatic hydrocarbons, BTEX (benzene, toluene, ethylbenzene, and xylene),  and atmosphere) by human activities such as petroleum exploration and drilling process, industrial 26 effluents, accidental spills, automobile releases, petroleum transport and depot storage, which causes 27 tremendous contamination over the cumulative period [7,8,9]. Pyrogenic, petrogenic, and 28 phytogenic emission into the atmosphere leads to high deposition of particulates on different surfaces. 29 Rainfall washes these particulates and gases out from the atmosphere. Several assessments have 30 shown that TPH influences inorganic parameters of water such as pH, temperature, dissolved oxygen, 31 total solids, and turbidity already reported [7,10]. A higher amount of these petroleum chemicals 32 reacts physiochemically and biologically across environmental matrices leading to the production of 33 persistent organic pollutants (POPs), micro particulates, and sediments triggering a high risk of 34 bioaccumulation in humans that may result in mental, genetic, immune, endocrine-disruption, 35 respiratory, teratogenic and carcinogenic effects [11,12]. Previous studies have focused on TPHs in 36 soil and sediment, aquatic species, and marine sources [13,14,15], while polyaromatic hydrocarbon 37 (PAHs) in soils and surface water of the region has received voluminous literature [16,17] and 38 consistently proved the negative impact to flora and faunas of the study area by organic emissions 39 from various activities previously enumerated above, however, we are not aware of any literature 40 evidence of TPH via atmospheric rainwater deposition in Nigeria, this forms the basis of our research. 41 The reason for this work is to i) to estimate the TPHs in atmospheric rainwater in crude oil and gas 42 region of Nigeria ii) source identification iii) evaluation of carbon preference index and average 43 carbon length and iv) non-carcinogenic risk assessment of TPH. 44 45 equipped with a flame ionization detector). The GC-FID column infused with HP-5 fused silica 23 capillary having dimension (30m  0.32mm  0.25m film thickness) with helium gas as carrier gas 24 at 1.75 mL/min flow rate. Appropriate calibration was conducted using hydrocarbon standard mixture 25 with integrated limit from C8H18 to C40H82 with five calibration-level prepared (10 -150 mg/L) and 26 injected into the gas chromatogram to obtain calibration curve of 0.99978 correspondingly. The 27 concentrated sample extract was injected in splitless mode using DCM as standard to remove 28 background interference to chromatogram area, as the temperature followed a stepwise process: 29 initial temperature (50°C) holds for 2 min, steady increase from 10°C to 100°C, holds for 2 min then 30 ramp at 5°C to 250°C and hold for 3 min, the final ramp from 5°C to 320°C and hold for 10 min [18].

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The final chromatogram results were analyzed with the Agilent software (chemstation).

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The contamination factor, CF is calculated to reveal the extent of aggregate TPHs contamination in 35 rainwater, while pollution load index entails the comparative means to assess the cumulative level of 36 TPHs for both aliphatic and aromatic forms using reference values Where, Cs = concentration of aggregate TPHs (mg/L).

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The formula, as shown above, was conducted for other aggregates respectively. ACL values are 34 usually constant in unpolluted rainwater samples but fluctuate as values deplete in polluted rainwater

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[27]. ACL was assessed for even n-alkanes in the environment to assess the anthropogenic impact in 36 the environment. Long-chain hydrocarbons are n-alkanes above n-alkanes at C26 usually from vascular plant-based 2 anthropogenic sources, while short-chain hydrocarbons are n-alkanes below n-alkanes at C26 from 3 phytoplankton or algae-based sources [28].
They are assessed using odd and even n-alkanes. For odd n-alkanes, LHC/SHC between 0 -1.00 6 shows phytoplankton, < 4.00 shows a mixture of phytoplankton and terrestrial plants, > 4.00 indicates 7 terrestrial plant inputs. For even n-alkanes, LHC/SHC between 0 -1.00 shows inputs from anaerobic 8 microbial biogenic sources, < 4.00 shows a mixture between anaerobic and anthropogenic petroleum, 9 releases > 4.00 shows that anthropogenic petroleum releases.

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It is the ratio of low molecular weight n-alkanes below C20, while above C20 gives the high 12 molecular weight used to determine the n-alkanes. L/H values close to unity (1) C w is the concentration of petroleum hydrocarbons in water (mg/L).
2 SA is exposed skin area: (2373cm 2 /day for adults and 3527cm 2 /day for children) 3 DAF is dermal absorption factor (unitless); (0.1 for adults and children) 4 ED is exposure duration; (25 years for adults and 6 years for children).

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BW is body weight; (80kg for adults and 15kg for children).

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AT is the average time for non − carcinogen = ED × 365 days 7 GIABS is a gastrointestinal absorption factor (unitless): (1.0 for adults and children).

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THQ is target noncancer hazard quotient: (1.0 for adults and children).

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IR w is ingestion rate; (2L day −1 for adults and 1L day −1 for children). The chronic daily intake obtained from eq. (6) and eq. (7) were used to obtain the hazard index for 12 non-carcinogenic TPHs as shown below: Where Hazard Index (HI) is the total of Hazard quotient (HQ) from dermal and ingestion, as the 15 acceptable limit is 1.0 [34].

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Hazard quotient is the probability that an adverse health effect is imminent (unitless)

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The reference dose (RfD) is shown in Table 2.     Table 11 shows the hazard quotient (HQ) of aliphatic and aromatic petroleum hydrocarbons (PHs) 24 calculated using the reference dose (RfD) as shown in Table 2 Table 12 shows the hazard quotient (HQ) of aliphatic and aromatic petroleum hydrocarbons (PHs) 29 calculated using reference dose (RfD) as shown in Table 2     (1) while that of O/E early rain was considered contaminated, other carbon aggregates were highly 5 present. Using PLI assignment, aliphatic hydrocarbons at R/R early rain were within safe background 6 level except for mid and late rain that were above one (1), indicating high pollution of atmospheric 7 rainwater, at Ogale (O/E), rainwater was highly polluted for all three rain periods but aromatic 8 hydrocarbons at both R/R and O/E were high and polluted as they were above one (1) [44]. The 9 contamination of water by TPH is associated with increases in particulate matter with fine particle 10 size, high temperature, reduced dissolved oxygen, low salinity, and anaerobic reactions [45]. In 11 addition, TPHs at higher carbon ranges are known to form oily films that prevent limited sunlight 12 penetration thus influencing poor water quality leading to taste and odour issues over some time.  alkanes, similar variation as seen in odd n-alkanes were attributed to slight anthropogenic input [49].

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The results of odd ACL vs CPI plots for early rain, mid rain, and late rain reveal that regression (   The average daily intake (ADI) of aliphatic and aromatic petroleum hydrocarbons aggregates was 4 assessed for ambient atmospheric rainwater from Rumuodomaya/Rumuodome (R/R) and Ogale

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In the atmosphere, where free chloride ions exist in the presence of ultra-violet radiation and high-29 temperature conditions permit ( The present study assessed total petroleum hydrocarbons (TPHs) in rainwater sampled via three 8 regiments (early rain, mid rain, and late rain) at Rumuodomaya/ Rumuodome and Ogale in Rivers 9 State, Nigeria. The TPH concentration at Rumuodomaya/ Rumuodome decreased from early rain to 10 late rain, while Ogale had a high concentration at mid rain, least for late rain that reveals the rainwater 11 were relatively contaminated and unsafe for human consumption from crude oil and gas processing 12 releases into the atmosphere and subsequently as rainwater. Chemometric assessment using total 13 petroleum hydrocarbon criteria working group standards showed that both aliphatic and aromatic 14 petroleum was relatively high. TPHs source identification showed that carbon preference index and 15 average carbon length gave correlation, which implies that contaminations were due to anthropogenic 16 sources, probably hydrocarbon been the major economic activity in the area. A risk assessment 17 conducted showed that hazard index was above one (1)  children were more at risk from continuous oral and dermal exposure to TPHs in rainwater.

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Government agencies with assistance from oil and gas stakeholders can set up a monitoring stations 21 for air, soil, and water contamination sources to assist in the development of a cost-effective approach 22 and remediation action plan to avert possible health issues in the future. The authors wish to thank BGI Laboratories Rumukwurushi, Rivers State, Nigeria for their technical 26 assistance during the research process.

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We have no special data information to declare, every data pertaining to the work is as presented in 29 the results

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Financial Assistance 31 We did not receive any financial assistance for this research work 32

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The authors declared no conflict of interest.  Brazil: a multi-parameter approach based on spatial and seasonal variability.  (2) Hydrocarbons and its Biodegradation. International Journal of Environmental Science National